Three dimensional graphics drawing apparatus for drawing polygons by adding an offset value to vertex data and method thereof

ABSTRACT

A three-dimensional graphics drawing apparatus includes a geometrical operation unit generating vertex data of a polygon, an offset register storing an offset value for the vertex data of the polygon generated by the geometrical operation unit, an offset operating circuit adding the offset value stored in the offset register to the vertex data of the polygon output from the geometrical operation unit, and a drawing unit drawing the polygon based on the vertex data after the addition by the offset operating circuit. Therefore, even with a geometrical operation unit having relatively low process performance, it becomes possible to draw a primitive which changes with motion, for example, at high speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for drawingthree-dimensional graphics and, more specifically, to a method and anapparatus for drawing three-dimensional graphics capable of providingdrawing effects such as motion, without the necessity of repeatingcomplicated processes including geometrical operations.

2. Description of the Background Art

Recently, in order to enable output of realistic and delicate images ona personal computer or a home use game machine, developments ofthree-dimensional graphics drawing apparatuses performingthree-dimensional image processing at high speed have been vigorouslymade. In a conventional three-dimensional graphics drawing apparatus,when a drawing primitive representing an object on an image plane is tobe moved, coordinates and the like of the primitive that change as theprimitive moves must be calculated by geometrical operations orcoordinate operation processes frame by frame.

An expensive geometrical operation unit having high geometricaloperation performance have been required in the three-dimensionalgraphics drawing apparatus in order to calculate coordinates and thelike of the primitive mentioned above at high speed. This resulted inthe problem of increased cost of the three-dimensional graphics drawingapparatus.

It may be possible to move the primitive by storing vertex data (vertexcoordinate data, color data, transmissivity data, texture mappingcoordinate data) of a polygon subjected to geometrical operation inadvance in an external memory and by drawing the vertex data frame byframe, rather than providing the expensive geometrical operation unit inthe three-dimensional graphics drawing apparatus. The amount of data ofthe moving primitive, however, is formidable, which means that anexternal memory of huge storage capacity is necessary.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and anapparatus for drawing three-dimensional graphics capable of drawing aprimitive that changes as it moves at high speed, with a geometricaloperation unit of relatively low process performance.

Another object of the present invention is to provide a method and anapparatus for drawing three-dimensional graphics capable of drawing, athigh speed, a primitive that changes as it moves, without necessitatingan external memory of a huge storage capacity, even when a geometricaloperation unit is not used.

According to an aspect of the present invention, the three-dimensionalgraphics drawing apparatus includes a geometrical operation unitgenerating vertex data of a polygon, an offset register storing anoffset value for the vertex data of the polygon generated by thegeometrical operation unit, an offset operating circuit performing anarithmetic operation on the vertex data of the polygon output from thegeometrical operation unit using the offset value stored in the offsetregister, and a drawing unit drawing the polygon, based on the vertexdata after the arithmetic operation by the offset operating circuit.

The offset operating circuit performs an arithmetic operation on thevertex data of the polygon output from the geometrical operation unitwith the offset value stored in the offset register. Therefore, bysuccessively updating the offset value stored in the offset register, itbecomes possible to represent motion or the like of the primitive.Therefore, even with a geometrical operation unit having relatively lowprocess performance, it is possible to draw a primitive that changes asit moves, for example, at high speed.

According to another aspect of the present invention, thethree-dimensional graphics drawing apparatus includes a reading unitreading vertex data of a polygon, which have been subjected togeometrical operation in advance, an offset register storing an offsetvalue for the vertex data of the polygon read by the reading unit, anoffset operating circuit performing an arithmetic operation on thevertex data of the polygon read by the reading unit using the offsetvalue stored in the offset register, and a drawing unit drawing thepolygon based on the vertex data operated by the offset operatingcircuit.

The offset operating circuit performs an arithmetic operation on thevertex data of the polygon, which have been subjected to geometricaloperation in advance, with the offset value stored in the offsetregister. Therefore, it becomes possible to represent motion of theprimitive, for example, by successively updating the offset value storedin the offset register. Further, as the vertex data of the polygon thathave been subjected to geometrical operation in advance are used, thegeometrical operation unit, which has been necessary in the conventionalthree-dimensional graphics drawing apparatus, becomes unnecessary.

According to a still further aspect, the method of drawingthree-dimensional graphics in accordance with the present inventionincludes the steps of reading vertex data of a polygon that have beensubjected to geometrical operation in advance, operating the read vertexdata of the polygon with an offset value, and drawing the polygon basedon the vertex data after the arithmetic operation with the offset value.

As the vertex data of the polygon that have been subjected togeometrical operation in advance are operated with the offset value, itbecomes possible to represent motion or the like of the primitive bysuccessively updating the offset value. Further, as the vertex data ofthe polygon that have been subjected to geometrical operation in advanceare used, the geometrical operation unit, which have been necessary inthe conventional three-dimensional graphics drawing apparatus, becomesunnecessary.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representing a schematic configuration of athree-dimensional graphics drawing apparatus in accordance with first tofourth embodiments of the present invention.

FIGS. 2A to 2D are illustrations representing processing of a primitiveby the three-dimensional graphics drawing apparatus in accordance withthe first and fifth embodiments of the present invention.

FIGS. 3A and 3B are illustrations representing processing of a primitiveby the three-dimensional graphics drawing apparatus in accordance withthe second and sixth embodiments of the present invention.

FIGS. 4A and 4B are illustrations representing processing of a primitiveby the three-dimensional graphics drawing apparatus in accordance withthe third and seventh embodiments of the present invention.

FIGS. 5A to 5C are illustrations representing processing of a primitiveby the three-dimensional graphics drawing apparatus in accordance withthe fourth and eighth embodiments of the present invention.

FIG. 6 is a block diagram showing a schematic configuration of thethree-dimensional graphics drawing apparatus in accordance with thefifth to eighth embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1 is a block diagram representing a schematic configuration of athree-dimensional graphics drawing apparatus in accordance with thefirst embodiment of the present invention. The three-dimensionalgraphics drawing apparatus includes: a geometrical operation unit 2receiving three-dimensional drawing data 1 defined by a world coordinatesystem in a program, and performing a series of geometrical operationson the three-dimensional drawing data 1; an offset register 3 holding anoffset value to be added to vertex data of each polygon constituting aprimitive; an offset operating circuit 4 adding (subtracting) an offsetvalue held in offset register 3 to (and from) the vertex data outputfrom geometrical operation unit 2; a drawing unit 5 performing a seriesof drawing processes based on the vertex data after the arithmeticoperation output from the offset operating circuit 4; a pixel memory 6storing pixel data generated by the drawing unit 5, as a frame image;and a display unit 7 displaying the pixel data stored in pixel memory 6.

A microprocessor, not shown, executes a program, and whenthree-dimensional drawing data (polygon definition) 1 is described inthe program, the three-dimensional drawing data 1 is output togeometrical operation unit 2. The geometrical operation unit 2 performsa geometrical operation on the three-dimensional drawing data 1, andprovides, onto a view port, vertex data of each polygon constituting acoordinate-transformed primitive, for example, vertex coordinate data.Offset operating circuit 4 adds, when the vertex coordinate data (X, Y,Z) generated by the geometrical operation unit 2 is input, an offsetvalue stored in offset register 3 to the vertex coordinate data andoutputs the result.

Drawing unit 5 generates pixel data of each polygon constituting theprimitive based on the vertex coordinate data after the addition of theoffset value output from offset operating circuit 4, and writes thegenerated pixel data to pixel memory 6. Display unit 7 reads pixel datafrom pixel memory 6 at a time when pixel data corresponding to one frameare written by drawing unit 5, and successively displays, so that themotion of the primitive can be represented with close resemblance.

The geometrical operation unit 2 includes: a modelingtransforming/visual field transforming unit 21 defining athree-dimensional shape to be drawn in a modeling coordinate system,transforming the three-dimensional shape defined in the modelingcoordinate system to the world coordinate system so that the shape isarranged in a space, determining projection conditions including aposition of a view point and a direction of a visual line for thethree-dimensional shape, and for transforming to a three-dimensionalshape in a viewing area; a lighting calculating unit 22 calculatinglighting of illumination of the three-dimensional shape after modelingtransformation/visual field transformation by the modelingtransforming/visual field transforming unit 21; and a perspectivetransforming/view port transforming unit 23 for perspectivetransformation of the object three-dimensional shape and transformingthe visual area to a view port.

Drawing unit 5 includes: a polygon set-up unit 51 calculating differencebetween vertex coordinates of a polygon to output an inclination betweenvertexes of the polygon; an edge generating unit 52 generating an edgebetween the vertexes of the polygon, with reference to the inclinationbetween the vertexes of the polygon output from polygon set-up unit 51;a scan line transforming unit 53 transforming each polygon pixel bypixel, based on the edge of the polygon generated by edge generatingunit 52; a pixel generating unit 54 generating pixel data in eachpolygon; a scissors test unit 55 deleting pixels not falling within adisplay frame; a stencil test unit 56 determining whether each pixel isan object of drawing or not; a Z comparing unit 57 comparing Z values ofthe polygon to determine whether the polygon is to be drawn on thedisplay image plane; and an a blending unit 58 synthesizing color dataof succeeding polygons with reference to an α value representing degreeof transparency.

FIGS. 2A to 2D are illustrations representing processing of a primitiveby the three-dimensional graphics drawing apparatus in accordance withthe present embodiment. FIG. 2A shows a polygon 9 constituting aprimitive before processing, which is drawn by three vertex coordinates10 to 12. When an offset value is added to the X coordinate of thevertex coordinate data of polygon 9 shown in FIG. 2A, then the vertexcoordinates 10 to 12 move to new vertex coordinates 10A to 12A as shownin FIG. 2B, and polygon 9 is translated along the X axis and drawn as apolygon 9A.

When the offset value is added to Y coordinates of the vertex coordinatedata of polygon 9 shown in FIG. 2A, vertex coordinates 10 to 12 moverespectively to new vertex coordinates 10B to 12B as shown in FIG. 2C,and polygon 9 is translated along the Y axis and drawn as polygon 9B.When the offset value is added to the Z coordinates of the vertexcoordinates of polygon 9 shown in FIG. 2A, vertex coordinates 10 to 12respectively move to new vertex coordinates 10C to 12C as shown in FIG.2D, and polygon 9 is translated along the Z axis and drawn as polygon9C.

In this manner, by successively updating the offset value stored inoffset register 3, it becomes possible to represent motion of theprimitive by shifting the vertex coordinate data of only such aprimitive that has motion.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, an offset value isadded to vertex coordinates of a polygon constituting a primitivecalculated by geometrical operation unit 2 and the result is output todrawing unit 5, so that the motion of the primitive is represented withclose resemblance. Therefore, different from the conventionalthree-dimensional graphics drawing apparatus, it is unnecessary torepeat geometrical operations on a moving primitive, so that high speeddrawing becomes possible, and hence, the speed of processing of theoverall three-dimensional graphics drawing apparatus can be improved.

Further, as the speed of processing of the overall three-dimensionalgraphics drawing apparatus increases, the geometrical operation unitallowing high speed geometrical operation becomes unnecessary, allowinguse of an inexpensive geometrical operation unit with relatively lowoperation processing performance.

Second Embodiment

The three-dimensional graphics drawing apparatus in accordance with thesecond embodiment of the present invention is similar in schematicconfiguration to the three-dimensional graphics drawing apparatus inaccordance with the first embodiment shown in FIG. 1, and differs onlyin that the object of operation by the offset operating circuit is thecolor data (R, G, B). Therefore, detailed description of theconfiguration and functions will not be repeated. In the presentembodiment, the offset register and the offset operating circuit will bedenoted by the reference characters 3 a and 4 a.

FIGS. 3A and 3B represent processing of the primitive by thethree-dimensional graphics drawing apparatus in accordance with thepresent embodiment. FIG. 3A represents a polygon 13 constituting aprimitive before processing, which is drawn by three vertex color data14 to 16. For example, when offset operating circuit 4a adds an offsetvalue stored in offset register 3a to color data 14 to 16 of thevertexes of polygon 13, the color data 14 to 16 of respective vertexesare changed to new color data 14A to 16A as shown in FIG. 3B. As aresult, it becomes possible for drawing unit 5 to paint the polygon 13Ain different gradation.

In this manner, by successively updating the offset value stored inoffset register 3 a, it becomes possible to make the overall color ofthe primitive darker or lighter, and the drawing effect of white-out orblack-out can easily be attained. Further, by adding an offset valueonly to any of R, G and B, it becomes possible to draw the sameprimitive in a color completely different from the original color.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, by adding an offsetvalue to color data of vertexes of a polygon constituting a primitivecalculated by geometrical operation unit 2 and outputting the result todrawing unit 5, the change in color is represented. Therefore, differentfrom the conventional three-dimensional graphics drawing apparatus, itbecomes unnecessary to repeat geometrical operations on the primitive,high speed drawing becomes possible, and hence the speed of processingof the overall three-dimensional graphics drawing apparatus can beimproved.

Further, as the speed of processing of the overall three-dimensionalgraphics drawing apparatus increases, the geometrical operation unitallowing high speed geometrical operation becomes unnecessary, allowinguse of an inexpensive geometrical operation unit with relatively lowoperation processing performance.

Third Embodiment

The three-dimensional graphics drawing apparatus in accordance with thethird embodiment of the present invention is similar in schematicconfiguration to the three-dimensional graphics drawing apparatus inaccordance with the first embodiment shown in FIG. 1, and differs onlyin that the object of operation by the offset operating circuit is thetransmissivity data (A). Therefore, detailed description of theconfiguration and functions will not be repeated. In the presentembodiment, the offset register and the offset operating circuit will bedenoted by the reference characters 3 b and 4 b.

FIGS. 4A and 4B represent processing of the primitive by thethree-dimensional graphics drawing apparatus in accordance with thepresent embodiment. FIG. 4A represents a polygon 17 constituting aprimitive before processing, which is drawn by three vertextransmissivity data 18 to 20. A different primitive 21 is drawn behindpolygon 17. For example, when offset operating circuit 4 b adds anoffset value stored in offset register 3 b to transmissivity data 18 to20 of the vertexes of polygon 17, the transmissivity data 18 to 20 ofrespective vertexes are changed to new transmissivity data 18 a to 20 aas shown in FIG. 4B. As a result, it becomes possible for drawing unit 5to draw polygon 17A with different transmissivity, so that primitive 21on the background can be seen through.

By successively updating the offset value stored in offset register 3 bin this manner, it is possible to change transmissivity of theprimitive, and therefore, it is possible to change the transmissivity ofa non-transparent primitive so that another primitive on a backgroundmay be seen through.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, by adding an offsetvalue to transmissivity data of vertexes of a polygon constituting aprimitive calculated by geometrical operation unit 2 and outputting theresult to drawing unit 5, the change in transmissivity is represented.Therefore, different from the conventional three-dimensional graphicsdrawing apparatus, it becomes unnecessary to repeat geometricaloperations on the primitive, high speed drawing becomes possible, andhence the speed of processing of the overall three-dimensional graphicsdrawing apparatus can be improved.

Further, as the speed of processing of the overall three-dimensionalgraphics drawing apparatus increases, the geometrical operation unitallowing high speed geometrical operation becomes unnecessary, allowinguse of an inexpensive geometrical operation unit with relatively lowoperation processing performance.

Fourth Embodiment

The three-dimensional graphics drawing apparatus in accordance with thefourth embodiment of the present invention is similar in schematicconfiguration to the three-dimensional graphics drawing apparatus inaccordance with the first embodiment shown in FIG. 1, and differs onlyin that the object of operation by the offset operating circuit is thetexture mapping coordinate data (U,V). Therefore, detailed descriptionof the configuration and functions will not be repeated. In the presentembodiment, the offset register and the offset operating circuit will bedenoted by the reference characters 3 c and 4 c.

FIGS. 5A to 5C represent processing of the primitive by thethree-dimensional graphics drawing apparatus in accordance with thepresent embodiment. FIG. 5A represents a polygon 22 constituting aprimitive before processing, which is drawn by three texture mappingcoordinate data 23 to 25. For example, when an offset value is added tothe U value representing the X direction of the texture mappingcoordinate data 23 to 25 of the polygon 22 shown in FIG. 5A, respectivetexture mapping coordinates 23 to 25 move to new texture mappingcoordinates 23A to 25A, and the texture of polygon 22 is translated inthe X direction and drawn as a texture of a polygon 22A, as shown inFIG. 5B.

When the offset value is added to V value representing the Y direction,among the texture mapping coordinate data of polygon 22 shown in FIG.5A, respective texture mapping coordinates 23 to 25 move to new texturemapping coordinates 23B to 25B, and the texture of polygon 22 istranslated in the Y direction and drawn as a texture of a polygon 22B,as shown in FIG. 5C.

By successively updating the offset value stored in offset register 3 cin this manner, it is possible to shift the texture mapping coordinatedata only for the texture of such a primitive that is in motion, so asto represent the motion of the texture.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, an offset value isadded to texture mapping coordinate data of a polygon constituting aprimitive calculated by geometrical operation unit 2 and the result isoutput to drawing unit 5, so that the motion of the texture of theprimitive is represented with close resemblance. Therefore, differentfrom the conventional three-dimensional graphics drawing apparatus, itis unnecessary to repeat geometrical operations on a moving primitivetexture, so that high speed drawing becomes possible, and hence, thespeed of processing of the overall three-dimensional graphics drawingapparatus can be improved.

Further, as the speed of processing of the overall three-dimensionalgraphics drawing apparatus increases, the geometrical operation unitallowing high speed geometrical operation becomes unnecessary, allowinguse of an inexpensive geometrical operation unit with relatively lowoperation processing performance.

Fifth Embodiment

FIG. 6 is a block diagram representing a schematic configuration of thethree-dimensional graphics drawing apparatus in accordance with thefifth embodiment of the present invention. The three-dimensionalgraphics drawing apparatus includes: a reading unit 9 successivelyreading vertex data of a polygon constituting a primitive recorded on anexternal storage medium 8; an offset register 3 holding an offset valueto be added to the vertex data read by the reading unit 9; an offsetoperating circuit 4 adding (subtracting) the offset value held in offsetregister 3 to (and from) the vertex data output from a geometricaloperation unit 2 and providing the result; a drawing unit 5 performing aseries of drawing processes based on the vertex data after thearithmetic operation output from offset operating circuit 4; a pixelmemory 6 storing pixel data generated by drawing unit 5 as a frameimage; and a display unit 7 displaying the pixel data stored in pixelmemory 6.

A microprocessor, not shown, reads and outputs the vertex data, forexample, vertex coordinate data of the polygon constituting theprimitive generated by preliminary geometrical operation from externalstorage medium 8 through reading unit 9. Offset operating circuit 4adds, when the vertex coordinate data (X, Y, Z) output from themicroprocessor is received, the offset value stored in the offsetregister 3 to the vertex coordinate data and provides the result.

Drawing unit 5 generates pixel data of each polygon constituting theprimitive based on the vertex coordinate data after the addition of theoffset value output from offset operating circuit 4, and writes thepixel data to pixel memory 6. Display unit 7 reads pixel data from pixelmemory 6 at a time point when pixel data corresponding to one frame arewritten by drawing unit 5, and successively displays, so that the motionof the primitive can be represented with close resemblance.

Drawing unit 5 includes: a polygon set-up unit 51 calculating differencebetween vertex coordinates of a polygon to output an inclination betweenvertexes of the polygon; an edge generating unit 52 generating an edgebetween the vertexes of the polygon, with reference to the inclinationbetween the vertexes of the polygon output from polygon set-up unit 51;a scan line transforming unit 53 transforming each polygon pixel bypixel, based on the edge of the polygon generated by edge generatingunit 52; a pixel generating unit 54 generating pixel data in eachpolygon; a scissors test unit 55 deleting pixels not falling within adisplay frame; a stencil test unit 56 determining whether each pixel isan object of drawing or not; a Z comparing unit 57 comparing Z values ofthe polygon to determine whether the polygon is to be drawn on thedisplay image plane; and an a blending unit 58 synthesizing color dataof succeeding polygons with reference to an α value representing degreeof transparency.

FIGS. 2A to 2D are illustrations representing processing of a primitiveby the three-dimensional graphics drawing apparatus in accordance withthe present embodiment. FIG. 2A shows a polygon 9 constituting aprimitive before processing, which is drawn by three vertex coordinates10 to 12. When an offset value is added to the X coordinate of thevertex coordinate data of polygon 9 shown in FIG. 2A, then the vertexcoordinates 10 to 12 move to new vertex coordinates 10A to 12A as shownin FIG. 2B, and polygon 9 is translated along the X axis and drawn as apolygon 9A.

When the offset value is added to Y coordinates of the vertex coordinatedata of polygon 9 shown in FIG. 2A, vertex coordinates 10 to 12 moverespectively to new vertex coordinates 10B to 12B as shown in FIG. 2C,and polygon 9 is translated along the Y axis and drawn as polygon 9B.When the offset value is added to the Z coordinates of the vertexcoordinates of polygon 9 shown in FIG. 2A, vertex coordinates 10 to 12respectively move to new vertex coordinates 10C to 12C as shown in FIG.2D, and polygon 9 is translated along the Z axis and drawn as polygon9C.

In this manner, by successively updating the offset value stored inoffset register 3, it becomes possible to represent motion of theprimitive by shifting the vertex coordinate data of only such aprimitive that has motion.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, an offset value isadded to vertex coordinates of a polygon constituting a primitivegenerated by previous geometrical operation and the result is output todrawing unit 5 so that the motion of the primitive is represented withclose resemblance. Therefore, the geometrical operation unit, which hasbeen necessary in the conventional three-dimensional graphics drawingapparatus, becomes unnecessary, high speed drawing becomes possible, andhence, the speed of processing of the overall three-dimensional graphicsdrawing apparatus can be improved.

Sixth Embodiment

The three-dimensional graphics drawing apparatus in accordance with thesixth embodiment of the present invention is similar in schematicconfiguration to the three-dimensional graphics drawing apparatus inaccordance with the fifth embodiment shown in FIG. 6, and differs onlyin that the object of operation by the offset operating circuit is thecolor data (R, G, B). Therefore, detailed description of theconfiguration and functions will not be repeated. In the presentembodiment, the offset register and the offset operating circuit will bedenoted by the reference characters 3 a and 4 a.

FIGS. 3A and 3B represent processing of the primitive by thethree-dimensional graphics drawing apparatus in accordance with thepresent embodiment. FIG. 3A represents a polygon 13 constituting aprimitive before processing, which is drawn by three vertex color data14 to 16. For example, when offset operating circuit 4 a adds an offsetvalue stored in offset register 3 a to color data 14 to 16 of thevertexes of polygon 13, the color data 14 to 16 of respective vertexesare changed to new color data 14A to 16A as shown in FIG. 3B. As aresult, it becomes possible for drawing unit 5 to paint the polygon 13Ain different gradation.

In this manner, by successively updating the offset value stored inoffset register 3 a, it becomes possible to make the overall color ofthe primitive darker or lighter, and the drawing effect of white-out orblack-out can easily be attained. Further, by adding an offset valueonly to any of R, G and B, it becomes possible to draw the sameprimitive in a color completely different from the original color.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, an offset value isadded to vertex color data of a polygon constituting a primitivecalculated by geometrical operation unit 2 and the result is output todrawing unit 5 so that the change in color of the primitive isrepresented. Therefore, different from the conventionalthree-dimensional graphics drawing apparatus, it is unnecessary torepeat geometrical operations on a moving primitive, so that high speeddrawing becomes possible, and hence, the speed of processing of theoverall three-dimensional graphics drawing apparatus can be improved.

Seventh Embodiment

The three-dimensional graphics drawing apparatus in accordance with theseventh embodiment of the present invention is similar in schematicconfiguration to the three-dimensional graphics drawing apparatus inaccordance with the fifth embodiment shown in FIG. 6, and differs onlyin that the object of operation by the offset operating circuit is thetransmissivity data (A). Therefore, detailed description of theconfiguration and functions will not be repeated. In the presentembodiment, the offset register and the offset operating circuit will bedenoted by the reference characters 3 b and 4 b.

FIGS. 4A and 4B represent processing of the primitive by thethree-dimensional graphics drawing apparatus in accordance with thepresent embodiment. FIG. 4A represents a polygon 17 constituting aprimitive before processing, which is drawn by three vertextransmissivity data 18 to 20. A different primitive 21 is drawn behindpolygon 17. For example, when offset operating circuit 4 b adds anoffset value stored in offset register 3 b to transmissivity data 18 to20 of the vertexes of polygon 17, the transmissivity data 18 to 20 ofrespective vertexes are changed to new transmissivity data 18A to 20A asshown in FIG. 4B. As a result, it becomes possible for drawing unit 5 todraw polygon 17A with different transmissivity, so that primitive 21 onthe background can be seen through.

By successively updating the offset value stored in offset register 3 bin this manner, the transmissivity of the primitive can be changed, andit becomes possible to change the transmissivity of a non-transparentprimitive so that a primitive on a background can be seen through.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, by adding an offsetvalue to transmissivity data of vertexes of a polygon constituting aprimitive calculated by geometrical operation unit 2 and outputting theresult to drawing unit 5, the change in transmissivity is represented.Therefore, different from the conventional three-dimensional graphicsdrawing apparatus, it becomes unnecessary to repeat geometricaloperations on the primitive, high speed drawing becomes possible, andhence the speed of processing of the overall three-dimensional graphicsdrawing apparatus can be improved.

Eighth Embodiment

The three-dimensional graphics drawing apparatus in accordance with theeighth embodiment of the present invention is similar in schematicconfiguration to the three-dimensional graphics drawing apparatus inaccordance with the fifth embodiment shown in FIG. 6, and differs onlyin that the object of operation by the offset operating circuit is thetexture mapping coordinate data (U,V). Therefore, detailed descriptionof the configuration and functions will not be repeated. In the presentembodiment, the offset register and the offset operating circuit will bedenoted by the reference characters 3 c and 4 c.

FIGS. 5A to 5C represent processing of the primitive by thethree-dimensional graphics drawing apparatus in accordance with thepresent embodiment. FIG. 5A represents a polygon 22 constituting aprimitive before processing, which is drawn by three texture mappingcoordinate data 23 to 25. For example, when an offset value is added tothe U value representing the X direction of the texture mappingcoordinate data 23 to 25 of the polygon 22 shown in FIG. 5A, respectivetexture mapping coordinates 23 to 25 move to new texture mappingcoordinates 23A to 25A, and the texture of polygon 22 is translated inthe X direction and drawn as a texture of a polygon 22A, as shown inFIG. 5B.

When the offset value is added to V value representing the Y direction,among the texture mapping coordinate data of polygon 22 shown in FIG.5A, respective texture mapping coordinates 23 to 25 move to new texturemapping coordinates 23B to 25B, and the texture of polygon 22 istranslated in the Y direction and drawn as a texture of a polygon 22B,as shown in FIG. 5C.

By successively updating the offset value stored in offset register 3 cin this manner, it is possible to shift the texture mapping coordinatedata only for the texture of such a primitive that is in motion, so asto represent the motion of the texture.

As described above, according to the three-dimensional graphics drawingapparatus in accordance with the present embodiment, an offset value isadded to vertex coordinates of a polygon constituting a primitivecalculated by geometrical operation unit 2 and the result is output todrawing unit 5 so that the motion of the primitive is represented withclose resemblance. Therefore, different from the conventionalthree-dimensional graphics drawing apparatus, it is unnecessary torepeat geometrical operations on a moving primitive, so that high speeddrawing becomes possible, and hence, the speed of processing of theoverall three-dimensional graphics drawing apparatus can be improved.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A three-dimensional graphics drawing apparatus,comprising: a geometrical operation unit generating vertex data of apolygon; an offset register storing an offset value corresponding to thevertex data of the polygon generated by said geometrical operation unit;an offset operating circuit performing an arithmetic operation on thevertex data of the polygon output from said geometrical operation unitusing the offset value stored in said offset register; and a drawingunit drawing said polygon based on the vertex data after the arithmeticoperation by said offset operating circuit.
 2. The three-dimensionalgraphics drawing apparatus according to claim 1, wherein said vertexdata includes vertex coordinate data.
 3. The three-dimensional graphicsdrawing apparatus according to claim 1, wherein said vertex dataincludes color data.
 4. The three-dimensional graphics drawing apparatusaccording to claim 1, wherein said vertex data includes transmissitivitydata.
 5. The three-dimensional graphics drawing apparatus according toclaim 1, wherein said vertex data includes texture mapping coordinatedata.
 6. A three-dimensional graphics drawing apparatus, comprising: areading unit reading vertex data of a polygon which has been subjectedto geometrical operation in advance; an offset register storing anoffset value for the vertex data of the polygon read by said readingunit; an offset operating circuit performing an arithmetic operation onthe vertex data of the polygon read by said reading unit using theoffset value stored in said offset register; and a drawing unit drawingsaid polygon based on the vertex data after the arithmetic operation bysaid offset operating circuit.
 7. The three-dimensional graphics drawingapparatus according to claim 6, wherein said vertex data includes vertexcoordinate data.
 8. The three-dimensional graphics drawing apparatusaccording to claim 6, wherein said vertex data includes color data. 9.The three-dimensional graphics drawing apparatus according to claim 6,wherein said vertex data includes transmissitivity data.
 10. Thethree-dimensional graphics drawing apparatus according to claim 6,wherein said vertex data includes texture mapping coordinate data.
 11. Amethod of drawing three-dimensional graphics, comprising the steps of:reading vertex data of a polygon which has been subjected to geometricaloperation in advance; performing an arithmetic operation on said readvertex data of the polygon using an offset value; and drawing saidpolygon based on the vertex data after the arithmetic operation withsaid offset value.
 12. The method of drawing three-dimensional graphicsaccording to claim 11, wherein said vertex data includes vertexcoordinate data.
 13. The method of drawing three-dimensional graphicsaccording to claim 11, wherein said vertex data includes color data. 14.The method of drawing three-dimensional graphics according to claim 11,wherein said vertex data includes transmissitivity data.
 15. The methodof drawing three-dimensional graphics according to claim 11, whereinsaid vertex data includes texture mapping coordinate data.